Complete biodegradation of atrazine by a microbial community isolated from a naturally derived river ecosystem (microcosm)

A microbial community, designated as AN4, capable of mineralizing the herbicide atrazine was isolated from a model river ecosystem (microcosm). The profile of degradation of atrazine by the AN4 community seemed to well reflect what occurred in the microcosm: rapid degradation of atrazine and transient accumulation of cyanuric acid, followed by relatively slow mineralization. The community comprised multiple phylogenetically distinct microbial strains, and the microbes were suspended and probably aggregated in the water phase of the microcosm. Denaturing gradient gel electrophoresis (DGGE) revealed that multiple bacterial strains exist in the AN4 community, and we successfully isolated two strains, which belonged to the genera Nocardioides and Pedomicrobium. Nocardioides sp. strain AN4-4 degraded atrazine to cyanuric acid and harbored the trzN and atzC genes encoding the s-triazine-degrading enzymes. This strain also degraded other chloro-substituted s-triazines like simazine and propazine, but it showed little degradability for simetryn (a methylthio-substituted s-triazine). Additionally, strain AN4-4 could grow on basal salt agar containing ethylamine or isopropylamine as the only carbon and nitrogen sources. Another strain, Pedomicrobium sp. strain AN4-9 could mineralize cyanuric acid alone. Therefore, we found that the coexistence of these two community members functionally serves to completely biodegrade atrazine.